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  • Author or Editor: Rasika G. Mudalige x
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Perianths of 34 Dendrobium Sw. species and hybrids were examined to elucidate the roles of pigment distribution and shape of upper epidermal cells in determining color intensity, perception, and visual texture. Color intensity was determined by the spatial localization of anthocyanin in tissue layers, i.e., in the epidermal, subepidermal, and mesophyll layers, as well as by distribution of pigmented cells within the tissue layer. Anthocyanins were confined to the epidermal layer or subepidermal layer in flowers with low color intensity, whereas they were also in several layers of mesophyll in more intensely colored flowers. Striped patterns on the perianth were due to the restriction of pigment to cells surrounding the vascular bundles. Color perception is influenced by the presence or absence of carotenoids, which when present, were distributed in all cell layers. Anthocyanins in combination with carotenoids resulted in a variety of flower colors ranging from red, maroon, bronze to brown, depending on the relative location of the two pigments. Four types of epidermal cell shapes were identified in Dendrobium flowers: flat, dome, elongated dome, and papillate. Epidermal cell shape and cell packing in the mesophyll affected the visual texture. Petals and sepals with flat cells and a tightly packed mesophyll had a glossy texture, whereas dome cells and loosely packed mesophyll contributed a velvety texture. The labella in the majority of flowers examined had a complex epidermis with more than one epidermal cell shape, predominantly papillate epidermal cells.

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Two full-length cDNA clones, Den-CHS-4 and Den-DFR-1, encoding chalcone synthase (CHS) and dihydroflavonol 4-reductase (DFR) were obtained from flower bud RNA of a lavender cyanidin-accumulating Dendrobium Sw. hybrid using reverse transcription-polymerase chain reaction (RT-PCR). Northern analyses indicated that both genes are expressed in all developmental stages of buds, with highest expression in the medium-sized buds. RT-PCR analyses showed that DFR expression was confined to floral tissue while CHS was expressed in floral and vegetative tissues but not in pseudobulbs. The nucleotide sequence of a DFR clone isolated from a pale orange pelargonidin-accumulating Dendrobium hybrid was exactly the same as Den-DFR-1, ruling out the substrate specificity of DFR as a possible cause of the color difference.

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